In communication systems, when transmitting a downlink signal, a base station performs the same precoding processing on the downlink signals in a frequency-domain resource corresponding to a precoding granularity, and the terminal device receives the downlink signal assuming that, in the frequency-domain resource corresponding to the precoding granularity, the same precoding processing is performed on the signal transmission.
For example, when the terminal device performs a channel estimation based on a Demodulation Reference Signal (DMRS), a frequency-domain channel interpolation may be performed on the channel estimation obtained from the DMRS in a frequency-domain resource on which it is assumed that the same precoding processing is performed, thereby improving performance of the estimation. The larger the precoding granularity, the larger the frequency-domain bandwidth that can be interpolated, and the higher the accuracy of channel estimation. However, since a channel is varied in the frequency domain, using a larger precoding granularity results in a lower degree of matching between the precoding and the channel, thereby limiting precoding gain. Therefore, the value of the precoding granularity is a compromise between the precoding gain and the performance of channel estimation.
In future wireless communication systems, how to determine a reasonable precoding granularity is an urgent problem to be solved.